The invention relates to a refractory nozzle for a metallurgical vessel, in particular for steel melts, having a flow-through opening with an upper end, a lower end and an inner wall that laterally encloses the flow-through opening.
Many of these types of discharge nozzles are known in metallurgy (see, for example, published patent applications: DE 195 26 970 A1, DE 196 18 605 A1, DE 196 51 533 A1, DE 196 51 534 A1, and EP 379 647 A2). One problem with these discharge nozzles is that they can be destroyed by the thermal stresses arising when the hot molten metal flows into them, or that metal is deposited on the inner wall of the discharge nozzles. In order to prevent this, the discharge nozzles are usually preheated. Gas burners or induction heaters are used to accomplish this. For example, in the case of gas burners, it is necessary that the preheating phase be terminated before the melt flows into the discharge nozzle, in order to be able to timely remove the burner from the flow-through area. However, the discharge nozzle cools during this transition period, so that the problems cited cannot be completely alleviated.
The objective of the invention is to improve the known discharge nozzles and to design the preheating stage such that destruction due to thermal stresses or solidification of molten metal onto the inner wall of the discharge nozzle is substantially prevented.
The objective is achieved according to the invention in that either a heater or a thermal insulating material that dissolves or burns when contacted by fluid steel, or a combination thereof, is arranged along the inner wall in the flow-through opening. A relatively slow temperature increase of the material of the discharge nozzle, when the molten metal flows into it, is thereby achieved. Thermal stresses are minimized, and a too rapid cooling and solidification of the molten metal that comes into contact with the inner wall are substantially prevented. It has proven to be expedient if the thermal insulating material is cardboard or a material with a melting point that lies below the melting point of steel. A material of this type causes any molten metal that may perhaps solidify onto it to be flushed out of the discharge nozzle along with the melt flow after dissolving or melting of the material, thus not alloying with the discharge nozzle itself. In an advantageous manner, the thermal insulating material is formed from a fibrous material or is sprayed on.
The heater is expediently made of a steel. Metals with a lower melting point than steel can also be suitable. When the discharge nozzle is used for steel melts, the heater dissolves itself as the melt flows through, so that the melt can flow unhindered through the discharge nozzle. Any material at first solidifying onto the heater is re-dissolved and flushed out of the discharge nozzle.
It is advantageous if the heater and/or the thermal insulating material is formed of at least two parts extending in the longitudinal direction and arranged next to one another in the radial direction of the flow-through opening, since it is easier to manufacture an arrangement formed in this manner. In the process, it is practical to form the two parts with the same shape so as to simplify the manufacture. Here, the parts should mutually touch or have a mechanical (and/or electrical) contact to one another.